Example: Tufte style axes in 3D

Tufte style axes in 3D. The axis affect is achieved by shifting axes,
ticks and labels.

The command \pgfplotspointouternormalvectorofticklabelaxis{x} is a shortcut
for \pgfplotspointouternormalvectorofaxis{\pgfplotsticklabelaxisspec{x}}.
The documentation for \pgfplotspointouternormalvectorofticklabelaxis is
missing in the reference manual.

Note that this shift is incompatible with the grid lines (by construction!).
To see this, try to add grid=major and you will see the the descriptions would be
slightly off.